This present invention relates to using velocity information. In particular, medical ultrasound is used to generate velocity information and/or related pressure gradient measurements.
Medical diagnostic ultrasound systems generate velocity information by Doppler processing. In the color Doppler technique for estimating velocity, an ensemble of transmissions and corresponding receptions to the same locations, such as 8 to 16 pulses along a scan line, are correlated to identify a phase shift. The ensemble size is large in order to achieve good signal-to-noise ratio and detection sensitivity. Large ensemble size in general results in low flow frame rate. Persistence is used to avoid flash artifacts. However, the persistence algorithm in general is not a good strategy in terms of temporal filtering the noise of the estimated flow. The ensemble occurs within a short time period such that the phase shift between adjacent pulses is likely constant. A velocity is estimated from the phase shift. An acceleration is then determined from a plurality of velocity estimates.
The velocity information may be used to identify pressure gradients. Pressure gradient in intraventricular regions and transmittal pressure drop have significant diagnosis implications for the assessment of ventricular load. Ultrasound Doppler measurement provides the velocity of blood flow, enabling the potential to estimate the pressure gradient. Pressure gradient is estimated using Euler's equation (i.e., the pressure gradient is proportional to the sum of the temporal velocity derivative and the velocity multiplied spatial derivative of velocity). A workstation was used after previously acquiring ultrasound color M-mode data. A color M-mode image provides a spatial-temporal velocity distribution along a scan line. By positioning the scan line along the inflow tract across the mitral valve and into the left ventricle throughout diastole, intraventricular pressure gradient may be estimated or indicated by processing velocity information.
Alternatively, a difference in velocity is calculated using a caliper function on a color M-mode image. Rather than using the pressure gradient, the left ventricular diastolic function may be assessed with measurements of the inflow velocities at the mitral valve. In yet another alternative, a high-fidelity pressure catheter read-out provides pressure gradient. Simultaneous volume measurements with the pressure gradient information are used to reconstruct pressure-volume loops. However, the use of a catheter is invasive and uses tedious tracing of ventricular contours.